Spectrochemical analysis system



April 20, 1954 M. F. HASLER ET AL SPECTROCHEMICAL ANALYSIS SYSTEM Filed Sept. 2'?, 1949 Sheets-Sheet l @Y JM@ Aprll 20, 1954 M. F. HASLER ET AL SPECTROCHEMICAL ANALYSIS SYSTEM 5 Sheets-Sheet 2 Filed Sept. 27. 1949 Nil IIIIII Ilmllll April 2o, 1954 Filed sept. 27, 1949 M. F. HASLER ET AL SPECTROCHEMICAL ANALYSIS SYSTEM 5 Sheets-Shee fis April 20, 1954 M. F. HASLER ET AL 2,675,734

SPECTROCHEMICAL ANALYSIS SYSTEM Filed sept. 27, 1949 l 5 sheets-Sheet 4 fs OPE.

April 20, 1954 M. F.v HASLER ET AL SPECTROCHEMICAL ANALYSIS SYSTEM 5 Sheets-Sheet 5 Filed Sept. 27, 1949 RECORDER ANPL|FIER.

.OOOOOOOOOOOO- Ex'cl'rA-rloN SOURCE Patented Apr. 20, 1954 UNITED STATES PATENT OFFICE 2,675,734 f SPECTROCHEMICAL ANALYSIS SYSTEM ration of California Application September 27, 1949, Serial No. 118,124

25 Claims.

This invention relates generally to emission spectrochemical analysis methods and apparatus, particularly of a type adapted to integrate spectrum line intensities and furnish an 'automatic recording of integrated line intensity ratios on concentration scales of various elements, s as to give direct-reading spectrochemical analyses. The invention will be hereinafter described in a specific illustrative form using electromagnetic radiations emitted from the sample of material by subjecting it to an electric spark or arc, i. e., of frequencies within the visible spectrum and known as light In perhaps the commonest form of emission spectrochemical analysis as heretofore known, a sample of the material to be analyzed is excited by subjecting it to an electric spark or arc, and a beam of the radiant energy so generated is dispersed by a prism or grating to form a spec-- trum, in which certain bright lines indicate the presence of particular elements, with the line intensities indicating the percentages or proportions of the velements present. The spectrum is sometimes recorded photographically, and in other cases the lines are reiiected to a phototube and brought to an indication by direct reading equipment Aassociated therewith. The.

direct reading equipment may comprise means for integrating the line intensities over a given time period, and for rendering an integrated reading at the termination of such period.

General objects of the present invention include the provision of improved direct reading methods and apparatus, including improved means for automatically making a recording of integrated line intensity ratios following a run on a sample of material. Further and more particular objects will appear in the course of the ensuing description.

In carrying out the present invention in an illustrative embodiment, a conventional spectrograph may be employed, of a type which forms a spectrum along a focal curve or "Rowland Circle. An array of receiver slits is positioned along this Rowland Circle to segregate a number of spectral lines from the spectrum. The light passing through -ea-ch of these slits is made to fall on ya narrow mirror which reilects it onto a detecting device, illustratively a multiplierphototube. Groups or these slits covering a small region of the spectrum are mounted on a single slit holder frame which can be moved along the spectrum a small distance. This allows profiling of any spectrum line and positioning of a group of vslits `in such a manner that all the light of each line passes through the corresponding slit and reaches the proper phototube. In this manner motion of the spectrum with regard to the spectrum base, or relative motion between slit groups, such as may be due to temperature change, vibration, or aging effects in the equipment, may be compensated.

With light from a particular line reaching each phototube, the next step is to integrate all the light received over a major portion of the sample excitation cycle. According to the present invention, this is accomplished by havingr each phototube charge a highly insulated condenser during a time period occupying a major portion of the excitation cycle. The condenser associated with each phototube and .spectral line is arranged for connection to an ultra-high-impedance amplifier and measurement or recording system (preferably a pen recording system operating on a strip chart). In the present illustrative embodiment of the invention, one of the condensers, associated with a phototube receiving light from an internal standard spectral line, is connected to this amplifier during the charging period, so that the amplifier follows the charging, and this continues until a predetermined value of charge is attained by this condenser. The recorder then actuates a microswitch which terminates the excitation source for the sample and ends the integration on all condensers. This feature has certain advantages, as will later appear, though it is not indispensible, since the charging period can simply be terminated after a predetermined time interval, as should be evident. Automatically the amplier and recorder are then switched from condenser to condenser, and the charge on each is recorded in sequence. Assuming the preferred pen type of recorder, this may be done on special strip chart paper printed with concentration scales for each element. These charts then provide a permanent direct reading record vof the concentration of each element analyzed in the sample.

Features of the invention include the provision, in connection with each integrator unit, of zero and sensitivity controls, which have several uses. By providing two condensers in each integrator unit and by storing the analysis of a low standard in one and a, high standard in the other, the,

amplifier can be switched back and forth between the two condensers and the zero and sensitivity controls adjusted so that the concentration scale exactly ts the standards. The zero control is also valuable for shifting the portion of the concentration scale to be used as the response from the optical background and the lower concentrations not required can be moved off the scale of the recorder.

The invention includes as another feature an automatic zero control whi-ch automatically compensa-tes for any Zero drift in the ampliiier, thus relieving the operator of any attention to this detail.

The invention will be described with reference Figure 5a is a detail taken on line 5cc- 5c ofi Figure 4; f

Figure 6 is a diagrammatic perspective View of a strip chart recorder' employed in the invention;

Figure'.7 shows a portion of a strip chart recording made in accordance with the invention; Figure 8* is 'a diagrammatic View showing, to exaggerated scale,l certain "slits employed in the invention;

Figure 9 is a schematic'diagram of the system of FiguresY land 2; and i Figure l0 is a schematic diagram oi the source unit, grating, and focal plane of a spectrograph.

In the drawings showing one illustrative embodiment of the invention (see Figures l, 2, 9 and 10), a conventional source unit is indicated diagrammatically at I0, and it will be understood that this unit is adapted to be energized through presently described circuiting from power mains II (typically 230 volts), and to producean electric spark or arc to excite the sample to be analyzed. For a preferred source unit, see United States Patent No. 2,417,489. It will be understood that, in accordance with standard practice, the radiant'energy from the excited sarnple is utilized to illuminate a slit, and that a beam of light from the illuminated slit is dispersed by a grating and brought to a focus in theY form of a spectrum extending along a focal lcurve or Rowland Circle. Such equipment conventional and need not be detailed herein. For a reference to a typical system, see United States Patent No. 2,420,077.

Along the focal curve are placed groups of slit assemblies such as indicated at I2 in Figures 3-5.` VThe details of th'ese assemblies will `be described hereinafter, and it will suice for the present to state that each slit group provides a plurality of closely grouped. individual slits i3, each slit being individually adjustable along the focal curve. It will be understood that these slits are positioned to aline with bright lines of the spectrum, the width of each slit I3 being greater than the width of a spectral line, and the slits being so centered that the whole of each line shows through the slot. Assuming spectral lines of .002" in Width, the slits I3 are typically made .006" in width. In addition, each slit group includes one monitor slit I4 of. somewhat greater width, e. g., .012", and in this case, the spectral line is centered with respect to one edge of the slit. i

Behind the slits are positioned narrow concave cylindrical mirrors I5 (Fig. 3) ladapted to 4 reilect the light passed through the slits to multiplier phototubes P1, Ps and Pm, the mirrors imaging the slits at the phototubes.

One phototube P1 is associated with an internal standard line. For example, assuming an analysis of stainless steel, a relatively strong iron line of the spectrum may be selected for the purpose of the internal standard, and the corresponding phototube will be designated as Pi. Alternatively, the primary reflected beam may be taken as the internal standard, as will be explained hereinafter; There may be a multiplicity of phtotubes Ps,"`o'ne for each spectral line of interestl For simplicity, only one such phototube Ps is indicated in Figures l and 2, but it will be understood that this illustrated phototube P5 is representative of arrnultiplicity of such tubes, and that the circuiting and selector switch positions to be described for the single illustrated phototube Ps will be duplicated for each additional phototube Ps that would be employed in an actual practical case. Such "a `plurality of phototube Ps is indicatedin the schematic diagram of Figure 9, which is representative of the same sys- 'tem'as Figures land 2,'but includes the additional phototubesPs and associated channels leading to amplifier input lead 3U, the equipment o f each channel'bet'ween the'phototube and relay RYZ being indicatedby the'block Ch. Finally, there is a single monitoring phototube .Pm, receiving lightfrom 'the monitor slit I4.

For convenience, the phototubes will' herein;H after be referred to"collectivelyas phototubes 'P,'

while in any instance in which there is the necessity for differentiating between the different phototubes', they will be referred to a'sPi, Ps or Pm, as the case may be. The same conventionwill be employed for certain later described condensers C and relays RY. i

TheV direct current power supply unit for the phototubes is conventionally indicated at IB, supplied with -volts alternating current. For

secure' necessary output. negative terminal of the `power supply unit is connected through sensitivity control resistors R2 to the cathodes of phototubes' P1, PS `and Pm. The

anodes of the phototubes Pr-PS and Pm are connected through suitable relays to highly insulated storage condensers C'I i, CIS and C Im, respectively. Leads 20 from the anodes of the photo-` tubes are connected to the movable contacts of phototube relays RYI i, RYIS and RYIm, and these contacts are normally closed against relay contacts grounded by leads 2l, as shown'. When these relays are energized, their movable con- I tacts close with contacts connected 'by leads 22 to the stationary contacts of condenser grounding relays RY`3i, RY35 and RYBI'nI The `movable 'contacts of these relays normally close with stationary contacts connected through resistorsRl to ground. The movable contact ofrelay RYB: is connected by lead 23 t'o the condenser Ch; while the movable contacts ofv relays RY3S and RYm are connected by leads 24 to thernovablecon-- tacts oi relays RY4S and RYAm. When the latter relays are energized, which is their normal condition, their movable contacts close with contacts connected to condensers CIS and Clm, the other sides of which are grounded, as indicated. The

movable contacts of relays RYIIS and RYMn close, when the relays are cie-energized, with contacts 4 connected by leads 25 t0 condensers C2.-J andC2m,.;`

and the. otherside of these condensers are also. electricallygrounded. Leads 22 also"c`onnectto the stationarycontacts of relays. RYZi, RYZS and' internal standard channelreceiving the. output from P1 and charging. up the condenserCli, one

or. .more sample analysis channels receiving. the

output'rfrom phototubefPS and charging up condenser `C|S, and a monitor.channel'receiving. the outputfrom phototube Pm and charging up the condenser Cm.

The lead 3|) from relays RY2 goes lto the input terminal'of a voltage amplifier A .of ultra high inputimpedance, `such as will. not preceptibly discharge the storage condensers.v This amplier may be of various types, but there is here shown an ultra-high impedance, amplifier of, the. bridge type. Accordingly,.the` lead 30,. is connected to the. control grid of thermionic amplifier tube 3| forming one arm .of '.the bridge amplifier circuit. A second amplifier tube 32 forms. a second arm of the bridge, .and the ancdes Yof these vacuum tubes 3| and32 arie-,connected to the bridge arms.

R6 and R1, said arms consisting of resistors, as indicated;.. andl preferably,.Y forY fine adjustment, a resistor R5 is inserted between resistor R6A and R1, and the bridge power lead 34 is connected to an intermediate point on resistor1 R5 by a vari-v able tap. While various tubes may beernployed for the purpose. of ampliertubes 3| ,and 32, an RCA PentodeNo. .959,4 electrometer connected, has been found suitable to. thepurpose. By electrometer connected is meant. that the tube element ordinarily employed. for the suppressor grid is usedas thecontrol grid, .and the element serving normally asthe controlgrid is tied directly to thelament. Accordingly, Yampliierinput lead 30v is connected to thetube element serving as the control grid .for tube 3|. tube 32 is connected to a zero control lead 35, referredto in more particularly hereinafter.

,'An amplifier power supplyunit 31, to which are connected l15-volt input leads 38 and 39, provides a ldirect current voltage, such as 95-volts,

between its positive and negative terminals 40 and 4|, and the aforementioned amplifier lead 34 is connected to positive terminal 40. Negative power supply terminal 4| is connected by lead 42 through voltage dropping resistor R|5 to the cathodeof one of tubes 3| and 32, which cathodes are series connected by lead 43. The two series connected cathodes are supplied with heating current through leads 44 and 45, the former of which is connected to negative -volt power supply terminal 45, and the latter of which is connected through voltage dropping resistor 41 to positive :20-volt power supply terminal 48. Positive 2U-volt terminal 48 is also connected by lead 49 to the screen grids of tubes 3| and 32.

Voltage dropping resistor R|5 is of such value as to result in the application of a D. C. voltage of about volts across the power input terminals of the bridge, i. e., between the cathodes of the two tubes and the center point between resistor arms R6 and R1. Voltage dropping resistor 41V lowers the 20 volt supply voltage to about 2.5 volts, so as to furnish each cathode with 1.25- volts.

Amplifier output leads 50 and 5| are connected across the bridge, between the resistors R6 and R1 and the adjacent amplifier tubes, `as indicated,

The control grid for..

6 and theseleads 5|) and 5| goto theinput terminals of a measuring instrument, preferably a recorder unit 52.. Whilevarious types of recorders may. be employed, vvithin the broad scope of the invention, that ,preferably used is of a well-known type adapted` to respond in accordance with voltage input, and to make a recording of voltage input on strip chart paper. A `suitable recorder for the Apurpose is Leeds and Northup O-50millivolt-Speedomax typeG strip chart recorder, and a recorder of this vtype is diagrammatically indicated in Figure 6 of the drawings. Such a recorder drives strip chart paper G from lower supply roller 53 between rollers such as indicated up and ,overV upper roller 54, .where it is engaged bythe'recording element, conventionally a pen, and -then down and under roller 53 to be rolled up by take-up roller 55. The shafts of the rollers 4 3 and 55v are chained together as indicated at y55, and the shaft of the upper roller is driven through a worm `51v and worm wheel 58 from a shaft 59 driven in turn through spiral gears 60 andv (ilI from shaft 62 The latter is driven through worm whee1,f63 and worm 64 from shaft -55' carrying worm wheel 66driven by worm 61 on the shaft of strip chart drive motor 56. Drivingly connected to the shaft 65, as by chain 69 and sprockets 10 and 1|, is a shaft 12 connected by worm 13 and worm wheel 14 to a shaft bearing a cam. 15 adapted periodically to actuate recorder microswitch S4. It willbe vseen that this microswitch will be actuated repeatedly as the strip `chart G is advancedby motor 68, the actuations occurring for example with each 1A advance of the chart. The complete mechanism and ycircuiting ofthe vstrip chart recorder will not be describedherein, since, as already mentioned, the details of suchrecorders are well known. However, the previously mentioned slide` wire potentiometer is incorporated on a drum llwhose movableycontact arrn8| .is carried on a shaft 82, this shaft carrying a large gear 83 driven4 throughsmaller gears 84 and 85 from drivemotor 86. In accordance with the invention, shaft 82 is provided, on opposite sides of gear 83, with cam disks 31 and 88 havingI switch actuating. notches89 and 95, respectively, ywhich coact with the movable arms 9| and 92 of microswitches S5 and S6,`Y A pulley 95 xed on shaft 82 has` wound thereonv a cord96 passing over four `idler pulleys 91, 98,99 yand I, and the stretch of cord between pulleys 99 and |05 eX- tends parallelwith the rupper chart strip roller 54, andhas secured theretothemovable pen unit IBI which carries pen |02 transversely across the strip chartpaper on roller 54 to make an ink line thereon ,and thus lrecord the position of the unit |01. j As shown, the unit is guided on a transverse` rod. |03. When the pen unit reaches its zero. position `(indicated in dotted lines in Figures 6), the'notch 99 in drum 86 comes opposite actuating arm 92 for normally open microswitch S6 closing the same. Notch 99 is made sufciently long that microswitch Siwill remain closed forksome V degree ofover-travel of the recorder pen below its zero position. As the pen moves toward the high end of the scale, the switch drums rotate clockwise, as viewed in Figure 6, through a little less than 365, until notch 89 in drum 81reaches the operating arm 9| for normally closed microswitch S5, and opens the said switch.

Manually adjustable zero controls are provided for the amplifier, vas, well as an automatic zero control for driftcorrection ci-rcuit which is operative, p rior to making a run on a sample, to f maintain the amplifier normally at zero 4output (in balance). Connectedto the aforementioned lead going to the control grid of amplier tube 32 is a lead 02 forming a circuit through the con-v The variouslater mentioned wiper arms at the difiere-nt levels or decks of this stepping switch Si are to be understood as operated by a single shalt itt, adapted to be pulsed or -ratcheted ahead, step by step, by successive energizations Of the rot y solenoid RYH). thevarious levels of this stepping relay are linked together by the dash-line 00, representing the fact that they are all operated by the common shaft Returning to wiper arm H14 otSIB, said arm is adaptedto close successively with a In the drawings.H

plurality of switch contacts connected to the variable airing or taps of potentiometer resistors Ri i, ofwhich there is one corresponding to Veach phototube. Opposite ends of vthese resistors RII are connected to leads l i0 and l i I, and the latter lead to power supply unit 31, where they connect with spaced points on a potentiometer resistor l i2 connected. between the positive and negative D. C. terminals l0 and t l. It will be recalled that the voltage across terminals and 1li is t5 volts.

Thetwo leads H0 and il!A are connectedto re-` sistor l I2 at points approximately l0 volts apart, with the more negative lead l I 0 at about 50 volts positive with respect to negative terminal 4 I. Re sister Il2 is grounded, as indicated at H4, at an approximate central point, in this instance at i volts positivewith respect to negative terminal (il, or in other words, half way between the two leads YI i0 and ill.

A. condenser Cil is connected between amplifier input lead 355 and lead 503, going therefore across snorting resistor R0 and the contacts of relay avi. de-energized, and therefore closed, a voltage tbe.- tween the variable tap of Ril and ground will be applied by way of lead 03, resistor R9, lead |02 and lead. Sii to the control grid of ampliiier tube t2. It will also be evident that at this time no voltage exists across condenser C4. By adjustment of zero control resistor RII the voltage so applied to the grid of tube 32 may be made such as to give zero output voltage between Wires 50, 5I leading to the recorder which will cause the latter to give a zero deection reading.

The two l0-volt power-leads H0 and III, of negative and positive polarity, respectively, are connected. to the two stationary contacts 0f`a relay the movable contact of which is normally closed with the stationary contact to which is connected the negative lead i I0. The movable contact ci this relay RYQ is connected through a lt may now be seen. that, with relay RYI very high. resistor Rill, of the order of 1,000 megohms, to the stationary contact of arelay RYB. The movable contact of the latter relay is connected to control. grid lead t6.

It will be recalled that pen recorder 42 contains a Zero switch S0, which is open at all times that the recorder pen is above the zero position, :but which is closed at the Zero position and below. Accordingly, when the recorder pen registers Zero, or goes oi scale below zero, switch S0 will be closed, and said switch will be open at any recorder pen position above zero. In the reset and ready-to-operate condition of the system,` relay RYB is energized and closed by later described circuiting, connecting the movable contact of relay RY9 via the high resistance RIU to condenserC4. Voltage across this condenserAv is continuously applied by lead 36 to the control grid fof tube 32. At this time the recorder pen V should register zero, but will tend to drift slightly above or below. At zero or below, switch S0 closed, and acts to energize relay RYB, closing the movable relay contact with the stationary 'Y contact connected to positive lead III, thereby causing the condenser C4 to charge and the control grid of tube 32` to go slightly more positive. This action slightly increases the positive output ofthe amplifier, and accordingly causes the ref corder pen to increaseits reading. Whenjthe recorder pen moves slightly above zero, s\`v i t ch. f

opens, cle-energizing relay RYB, so that the movable contact of the latter closes with negative lead IIIl, with the result that the condenser C'4 slowly discharges and reverses polarity so that the V control grid of tube32 goes negative, the amplifier output goes negative, and therecorderpen re turns to zero, orjvery slightly below.

In this way, at the reset and ready-temperate. position ol the system, the recorder pen constantly hunts between a positionr very slightly above zero and a position veryslightly belowzero, and does not drift substantially from Zero atany time.

It may here be mentioned that while the first position resistor RI I is normally adjusted to es tablish a zero position for the recorder pen with the amplifier input terminal grounded, other .resisters Ril may, if desired, be adjusted to Athrow the zero position ofthe pen far oil-scale, for a purpose which willappear hereinafter,

With the systemat reset and ready-to-opcrate condition, a high resistance resistor RIZ, of the order of 5,000 ohms, is connected across the amplilier output leads going to the recorder. This resistor devel-ops a large voltage change across the recorder for a small change in the balanced condition (zero output) of the amplier, and hence magnies any tendency for the -recorder pen tohunt above and below its Zero position.

Under these conditions the effectiveness of the above described automatic zero control circuit.

is maximized.

As shown in the drawings, amplifier outputl lead 5i) has connected thereto lead I 20, fromv which a branch lead l2I goes to one end of the described resistor R12. The other end of this resistor is connected to the lower stationary con-l tact of relay RYI i, and the movable contact arm of the latter is connected by lead |22 back to the other amplifier output lead 5i. The upper sta tionary contact arm of relay RYII is connected by lead I23 containing 250 ohm resistor RI3 to the wiper arm 25 of stepping relay RYII). This arm I25 makes successively with contacts connected to the adjustable arms or taps of 1,000

ohm resistors Rt, and the latter are connected to the amplifier output lead |20. At reset and ready-to-operate, relay RYiI is energized, and RIZ therefore connected across the amplifier output circuit 50, 5I leading to the recorder. In operation, with the source unit energized, the relay RYII is de-energized by energization of relay RYZI, in a manner later to be described, and therefore connects sensitivity control resistor R8, of the order of 1,000 ohms, together with 250 ohm resistor RIS, across circuit 50, 5I. Adjustment of the resistors RYB thus adjusts the recorder sensitivity as desired for any given am-A plifier output current.

Before proceeding further with the detailed circuit connections 'ofthe system, particularly those employed to energize the various relays, the general operationof the system may now be described. The relays are all shown in the drawings'in their cle-energized positions. With the system inthe resetand ready-to-operate position, they relays are all in the positionshown eX- cepting relays RY4,RY5, RYB, RYI I', RYIS and RY24,`wl iich are energized and closed, and selector switch SI is in its rst position, as are the subsidiary switches SIA, SIB, etc., which operate with Sl To start an analysis, the operator 'starts the excitation source unit lil. Through'later described circuiting, this operation results in'closing RYI, RY3,"RY26,RY2I, RY23, and RY25. The action of relays RYI and ,RYS connectsV the phototubes to the corresponding condensers Ch. CIS and CIm. In the case of condensers Cs and CIm, the energizing circuit for the condensers `includesalso the movable` and lower stationary Ycontacts ofthe relays RYS 'and RYm, as will j be seen. `All phototubes to be used are connected `in'this way `by duplicates' of the abovecircuits ,j whenwthe source 'unit is started, it being understood that there maybe amultiplicity of the phototubes Ps and relay circuits leadingtocondensers such as CI s.

Also; as the 'sourcefu'nit is started, relay RYi is energized `and locked closed byrelay lock'IEl, thereby 'opening' the Yenergizing circuit for relay RY5; Vcausing amplifier inputlead 3|) to be un- 'n grounded by vopening'tlre contacts` ofirelay P035. Normally, with thesystem in the reset and readyto-o'perate condition,` Vrelay 'RY is energized,

closing itsA contacts and Vthereby grounding the `ampliiier. Alsofas'the source unit is started, RYZi is energized,- connecting CIil to amplier input lead 30. This'enei'gization of relay RYi is effected through a lead' It! connected tothev iirst position contact of a deck switch SIE ofstepping 'switch Si. Thewiper arm IM of this switch SIE is'cOnne'ctedby lead IliZto a low voitage 'direct'current power supply lead |43," carrying typically 28 volts,"this leacllll going to a positive Vterminal of 28--volt direct current power' supply unit |44. The operation of relay RYZ Iv alsoopens lead |415 which h asbeen 'energizing vrelay RYS, so that the 'latter opens', breaking circuit* 35 'and therefore` disconnecting'the automatic zero conf trol circuit. TheleadjIS that energizesrelay RYSl is connectedjthrough"relay'RY2I 'to lead |45a. going to a'iirstposition contact of a deck switch'SID or stepping switch`S|,`the wiper arin i |4527' of saidswitcli- SID beingcnnected to 28- i volt power supply line |43. 'ThusV it will be seen that the automatic zero control circuitl can be operativeronly in the'nfumbei" one' position 'of the stepping switches, and then only priorto energization of relay RYZI whichcloses thsource unit as will be. described. liktthesame time-,also by reason of energizationfof relay RYEI, acting through' circuit lead |45 andbranch lead |153,

, relay RYI Il is deL-energized', removing resistor Rig from across the ampliiier output circuit and con- 110 that C Ii is not only being charged from its phototube, but is connectedthrough RY2i to the amplier. It should also be recalled that because of the ultra high impedance of the amplifier A, the voltage developed across the condenser C|i` is utilized without perceptible dissipation of the charge flowing into the condenser. in this connection, it will be evident that the circuits connecting the condensers to the amplifier must be so designed as to avoid dissipating the charges of the condensers. The described circuits connecting the condensers to the amplier may be characterized as having ultra high or innite shunt impedance. The time taken to actuate the recorder to full scale deection can be adjusted by means of the sensitivity control R8 and the attenuator R2. At full scale, the recorder actuates switch S5, the latter, in the present embodiment of the invention, being normally closed, and being opened 'at the` full scale position of' the recorder I9. Action ofthisl switch S5 opens relays RYIi, RYIS, andRYIm, thus immediately disconnecting the phototubes from ltherespective condensers and at the same time connectingk the phototubes to ground. Tracing the circuit connections from switch S5 to relays RYI, the one side of switch S5 is connected via leads |42 and |43 to the 28-volt power supply, while the other side of said switch is connected via lead |50, the contacts of relay RYZE] (then closed), and' lead "I`5I to the several relays RYILRYIS, and'RYJm. Hence, opening of full scale recorder switch S5 instantly de-energizes the said relays, disconnecting the phototubes from the condensers, and connecting them to ground. i

Opening of switch S5 also, through lead |50, and switch SI5, de-energizes integration termination relay RYI9, which in turn, 'through its 'several contacts, and later described circuiting, opens relays RYI'I, RY23, RY24, RY25, and RYZU, disconnectingthe source unit and so completing the integration termination. It should'here be yexplained that opening of relay RY23 de-energiz'es relay RYZI, its contacts being in the energizing circuit for. RYZI. Said relay RYZI s remains closed, however, until' its lock l is released, as

presently to be described.` RY2I), upon opening,

"tained' avalie, which, when,amplified,A gives aV i "full scale'reading on recorder 52,it'bei'ng' recalled 75` de-energizes relays RYI, resulting in connecting thephototubes to ground. And the opening'of relay RYIT de-energizes chart drive inotor` relay RYI5,-though the latter remains locked closed until released by energization of release coil 237.

The de-energization of relay RYI 9 upon termination of integration closes relay contacts connected to leads |54 and |55, lead |54 being connected to a lead |56 going to the positive terminal of 28-volt power supply unit |44. Lead '|55 goes to relay RYI 1, which is accordingly energized and closed. The movable contact of RYI'L' jthen closed with the stationary contact 'of saidrelay, is connected via lead |66 to alead ltcohncted in turn to one side |63 of 11S-volt alternating current supply line |63',`| 64. The stationary con- "tact of relay RYI'I isconnected by way of lead I65,^the contacts of normally closed relay'RYIB, lead |66, relay RYI5, and lead |61 tothe other side |64 of the ll-voltpower line. The power line lead |64 is the neutral'side, and is grounded,

' as indicated at |68.

Thev described energization of relay RYI l closes the circuit to relay RYI5, closing the latter, and thereby closing its movable contact against its lowerstationary contact, which results in supplying 11B-volt alternating currentvpower to the drive motor 68 of the strip chart recorder. Thus,

the movable contact of relay RYIE is connected to lead I'Iil going directly to recorder chart drive motor B, while the lower stationary contact of relay RYIE is connected to lead 3S connected in turn via lead |13 to the live side |53 of the 115- volt power line. Relay RYI is locked closed by relay lock Ibla. The neutral side |64 of said power line is connected to previously mentioned lead 38, having branch lead H3 entering the re corder and connecting to the other side of recorder chart drive motor E5, as well as furnishing power to one side of recorder motor 85, and one side of the recorder amplifier Af. In passing, it may be mentioned that the other side of amplifier Ar and the other side of recorder motor 8S are furnished with power from lead Il5 connected to live power lead 39. It may now be seen that energization of relay RYI 5 acts through its movable contact and its lower stationary contact to connect 11E-volt power to the chart drive motor |58, which accordingly operates to advance the strip chart.

As the chart drive operates, recorder microswitch Slt is momentarily and repeatedly closed by cam '|5, this closure occurring on each quarterrevolution of the latter, applying the 28volt power from leads |42 and 43 to a lead |80 going through manual switch S3 to the coil of relay RYI3, closing the contacts ofthe latter momen tarily to send a 23-volt pulse from lead |42 to lead |8I, thence through the movable and upper contacts of then deeenergized relay RYM to a lead |82 which connects to the solenoid RYIil for stepping switch SI` This solenoid RYIB for switch SI may be of Various types, but that preferred is a rotary solenoid stepping switch of the type manufactured by G. Il. Leland, inc., under the trade-mark Ledex, and comprisesa rotary shaft (the aforementioned shaft |05) vcarrying a plurality of contact arms at different levels along the shaft (such as aforementioned contact arms |04, |25 and IlI) for a corresponding 'plurality of rotary switches, 'each such contact arm being arranged to sweeper wipe 'around a circularly arranged set of contactsmounte'd on disks or wafers at the said levels. Ihe shaft is advanced through the angle'betw'en contacts by' a suitable ratchet mechanism on each energization "of a ron tary type of solenoid. The switch includes also a normally closed switch in the energizing circuit for its solenoid which is opened 'just'at, or just before, the end of the' power stroke of tlie solenoid.

' Such a switch is indicated at Sl inF-igg'ure'Z.` The relay also includes are'siston'connected in shunt with switch Sl and which carries a reduced current to the solenoid to lhold thesanie temporarily at the forward end of its'str'oke yfollowing the opening of switch S1. `Such rotaryv solenoid stepping switches are'well' known' in the'artY and hence need not be further described herein. The

energizing lead I2 going to this'so'lenoid RYIG is connected thereto through 'the switch S1, and the resistor Rl is ina shunt circuit with switch Sl, which circuit also includes'a normally closed pair of contacts of a relay RYI?. llhus, the'current pulse caused by closing of S4 flows through S1 to the solenoid Rifle, actuating the switch SI to step ahead to position 2.

This operation of stepping switch SIA causes wiper arm I4I of switch SIE to open circuit "|46 leading to relay RYZ, thereby disconnecting the internal standard channel from amplifier input lead 3U. -The wiper arm |4I of'switch SiE'now closes'with a second position contact connected .by lead |85 --to'relay'RY2s,'energizing the latter and so connecting sample channel lead 22 to amplifier input lead 30, thereby applying the voltage on CIS in the second or unknown sample channel to the amplifier. At the same time, the wiper arms |25 and m4 of stepping switches SIC and SIB move to their second positions, selecting a second pair of sensitivity and zero control resistors Rs and RII which are connected to the recorder and ampliiier, respectively. Thus, the voltage on condenser CIS will be recorded in the saine manner as the recordation of the voltage on C I i, but using a diiierent sensitivity and zero point if so desired. The zero point can, in fact, be placed ori scale, and a high range of interest expanded over the full recorder scale by proper operation of the zero control and sensitivity control resistors.

Thus the voltage on CIS is applied to the arnplifier, and after amplification, to the recorder, this taking place without perceptible discharge of the condenser. After a dwell, sufficient to allow the recorder pen to reach and dwell at the indicated reading (which may be a time period of one to two seconds), the selector stepping switch SI will be pulsed by closure of recorder switch S4, as before, switch SIE movingtol its third position, and sending current via a line |89 to relay RYZm. The voltage on the condenser in the third channel will then be recorded, again with different sensitivity and zero settings, if desired. If but a single sample channel is employed, of course, as in the simplified schematic showing here given, the third channel will be the monitor channel. However, in practice, there would normally be a multiplicity of channels, for the various elements to be determined, and corresponding successive recordings of the voltages on the several charged condensers.

The reading obtained on the recorder is related linearly to the voltage on the condenser, which is proportional to the total output of the phototube, and this in turn is proportional to the total intensity of the spectral line illuminating the phototube. The voltage on the condenser is also, of course, proportional to the time of charge. This time is controlled by the output of the internal standard phototube, so that the integrated intensities recorded are, in reality, integrated intensity ratios of the element lines to the internal standard line. By a proper calibration of these integrated intensities against samples of known concentration, recorder scales can be set up to read concentration percentages directly for each element to be analyzed, and such scales are conveniently and preferably printed or otherwise lettered directly on the strip chart paper (see Figure '7).

To automatically terminate 'the recording and reset for the next analysis, the following provisions are made:

A reset deck switch SIF on stepping switch SI has wiper arm ISB movable over a set of contacts which include two contacts in addition to the number employed on the other switch decks, giving two positions beyond those employed on the other decks. Operable in conjunction with the switch SIF of the last mentioned switch deck is a double pole rotary manual switch S3 comprising two rotary switch arms 200 and 20| on a common shaft 232, these switch arms having a multiplicity of positions, in the present case three, as indicated. The first position contact of switch SIF is not used. The second position contact for switch arm |90 is connected by lead 203 to the rst position contact of switch arm 200. The third position contact for switch arm |90 is connected by branching leads 254 and 205 to the first position contact and the second position contact for switch arms 20| and 260, respectively. The fourth position contact for switch arm ISG is connected by branching leads 206 and to the second position contact and third position `contact for (switch arms, 2st and 200, respectively. Finally, the fth position contact for switch arm Ieiilis connected by lead 268 to the third position contact for switch arm 2iiI. The arms of switch S3 are manually moved to the position number which corresponds to the number of the lastl channel :desired to be recorded prior to automatic reset. k,'Ihen, when thev arm |90 of stepping switch SBF! reaches the first position beyond the position number of the last channel to be'rec'orded, a series of automatic reset operations occur, to be followed, when switch SIF reaches its next position, by the completion of the automatic reset operations. Assuming, for exampld'tha't it should be desired to' terminate integration' and reset the system at the end vof the second channel recording, that is to say, immediately after 'recording the charge o'n'condenser CIS, 'switch'arnis ile'iii and 28| are moved to the secondposition contacts, as shown. Then, upon the switch arm Iii@ reaching position three, the following operations will then automatically occur. The Zit-volt power in line 43 will flow via branch line 2 I Ii vto arm it@ of switch SIF, thence throughlead 205 to switch arm 200, and then Via line 2H to'energize and close relay RY22. This closes a circuit consisting of lead 2|2 from powerl line |54 to the release coil 2|3 of relay RY2 I from there to the closed contacts of relay RY22 and from there via lead 2 l #l to lead IBI going back to the other side |63 of the power line. Relay RYZ l, being already cie-energized upon opening of recorder full scale switch S5, is accordingly released, and this has the effect of de-energizing relays RYi, RY3S, and RYSm by breaking lead 220, said relays having previously been energized through the lower stationary and movable contact of relay RYZI from a lead 22| connected to a 28-volt power supply lead |43. De-energization of relays RY@ has the eifect of connecting condenscrs CIi, etc., to ground through resistors Ri, thus discharging them completely.

Unlocking of Arelay RY2| at the same time con-- nects ils-volt iead 22 through the relay contacts to a lead 225 going to the coil of relay RYS, which closes its contacts to connect amplier input lead through resistor R3 to ground. The amplier, as well as the storage condensers and the phototubes, are thus held at xed ground potential at .the reset and ready-to-operate position.

I n addition, the unlocking of relay RYE! operatesthrough its two upper contacts to connect conductor to conductor I45a, the former leadingto relay` RYB, and the latter to the rst positionV contactxof switch Sil) of selector switch SI. Relay RY is not yet energized, however, and will not be until the wiper arm ib of switch SID returns to its Iirstposition contact, andthe automatic zero controlY circuit accordingly remains inactive until such event.

The above operations alloccur upon the wiper arm |90 of switch ,SIF reaching its third position contact, with the arms of switchSsat their second positions, yas aforesaid. yUponreaching the` fourth position contact,` furtherreset operatie, geen. as, follan# The aie/.dlt power.

from lead 2| 0 passes through switch arm |90 ofgswitch SIF to the fourth position contact. thence viaflead 2136 to switch arm 20|, and from there by way of leads 235, 2350i and 235 to relay RYIB, which thereupon closes. This closes a circuit consisting of lead |6| from power line |63, the c ontacts of relay RYIJ, the release coil 2310i relay RYI5, and lead ll back to power line ,lead Hill Relay RYIS is therefore released, The movable contact of RYIE accordingly separates from the relayrcontact connected to lead 3g, thereby breaking the energizing lead |10 for the chart drivernotor 63 from its connection with the'r live power circuit leadV |53. At the same tirndthemovable contact'of relay RYI5 connected to leadfllil closes with a contact connectedto alead 269 connected to 28-volt 4direct currentnpowersupply,lead M3, lead 2Q@ including a filter such as the combination RIT, RI8, 28 -,volt direct current power is thus applied to the alternating current motor `6B of thdrecorder, which serves to brake said motor and' to stop the same, instantly. It is a fact fam ivarmto those skilled in the art that the appli@ tion. @indirect curlentvoltase to anal.-u ternatingcurrent motorwill serve as an eifectivel brake.l The chart drive motor G8@Y O the reeprderisthus instantlystopped., No further ac 'u ationof recorder pulse switch Sd will thereforeoccnr, andthe p ulseswiiicnhave ,been de: livered to the Stepping; relay ,coil l l1 4accordinely Cease., .Y i At thewsame` time, the current in, line 235a flows to theoil .of relay RY |,fi,;cau sing, its mov: able-...Contact t0. separate from, the.. stationary Contact tqwhichv the stepping switch energizing 1ea 1l.,f.| ;8i`Y is connected, thereby disconnecting switch land solenoid RYlifrom lead ISI coming froinRYi which 4is energized by recorder pulseswitch -Sii. m,The actionl yof RYIS connects leadgjt to the;-28 volt source lead |43. The energizedline 2355 also,through lead 24d, energizes-,t-he coil-or^` relay RYIZ, the circuit being completedtogrouncl byway of lead 213|, a stationary switchcontact 242 of switch SI, and a notched, electrically grounded disk 243 or collector ring of switch SL The disk 2513 will be understood as occupying one of the levels on the` shaftl-lof stepping switch Si, and it will bie-.iunderstood;thatv this disk is fixed to and turns Awithshaft |95, step by step, in accordance withthe ratchet action caused by intermittent energization of solenoid RYIt. At one position irithe periphery of disk 243 is a notch 255 givirlagclearance between stationary contact 242 and,` the..A disk:A 23. Notch 225 registers with stationary contact 242 in the first position of the stepping switch Si, i. e., the position of the common shaft |05 in which the Various wiper arms of the switches SIB, SiC, etc., close With their rst position contacts. [it the time under consideration, the disk 243 will be at a position with notch 24:3 out of registration with contact 242, so that the circuit from lead 24| will be closed thrOllgh Contact 232, disk 243, and a grounding contact 246.

Energization of relay RYI2 results in connecting 28-Volt lead 2|@ through the lower stationary and movable contacts of relay RYIZ lto lead the circuit continuing through lead 2350i and branch lead 250 to the relay coil of RYM and thence to ground. .Relay RYI2 thus locks itself closed, and its action alsorlocksr closed the relay RYI 4. This action of relay RYI 2 also vsends vthe ,w28-Volt powerv from lead 235 through-wire 25| to a stationary relay contact then closed with the upper movable contact of the relay RYIZ, which is in turn connected by wire252 to switch S1 of the selector switch. It should also be noted thatthe upper movable Contact of relay RY|2 has open circuitecl the switch shunting resistor RIG. 28 volts of direct current power are accordingly continuously applied through switch S1 to stepping switch solenoid RYIB. The result of this is that thesolenoid RY| continuously operates the stepping switch SI until the various switches SIA, SIB, SIC, etc., have all been stepped back to the number one position illustrated in the di-` agram. This homing action results from the fact that at the end of each stroke of the solenoid,- the switch S1 opens to allow the solenoid to return, the shunt holding resistor RIS being at this time open-circuited.

Arriving at the number one position the notch 245 in disk 243 opens the circuit by which the coil of relay RYIZ is being energized, and the relay is accordingly cle-energized, disconnecting the 28-volt power source from RYIU. Opening of ,relay RYI 2 at the same time cuts oil the power supply to relay RYHI, and the latter is therefore simultaneously de-energized. Lead |8| is accordingly again connected to RYIU through switch S1, but since the chart drive motor has been stopped, no further pulses will be received. The rotary solenoid selector switch has accordingly been reset in its starting position.

The circuit connections and relays by which the source unit is connected and disconnected are as follows. A 230-volt line is connected to the primary winding of a step-down transformer T, the secondary of which has connected thereto circuit leads 26D and 26|- connected to the lower movable and stationary contacts of relay RYlii, while in series with lead 26| is the coil of relay RY24. The two movable contacts of relay RY25 are connected across power main leads Ila and lib by wires 252 and 263, respectively, and wire 263 is connected by wire 264 to the stationary contact of RY24, while the movablevcontact oi the latter is connected by wire 265 to the coil of RYZS. The other side of the coil of EYES is connected by lead 256 to relay RY23, and from the latter the circuitcontinues via lead Ztl' to the stationary upper contacts of RY25. The lower stationary contact of RYZS is connected to lead 266. The upper stationary contact of RYZt is connected by lead 210 to one side of the source unit, and the other-side of the latter is connected by lead 21| to lead 266. A `starting switch SI1 is placed in a lead 214 connected between wire 256 and the power line lead IIa.

iin the reset and readyto-operate position, relay RYiQ is being energized through lead |50 going to normally-closed full-scale recorder switch S (being the switch automatically opened when the recorder pen reaches the high end of the scale), the circuit continuing thence via lead |42 and |43 to the 28-volt direct current power supply. Relay RYiQ is accordingly energized, its contacts have closed the circuit 25d, 25|. Relay Rl'Zii is therefore also energized and closed. Operation or" starting switch Sil sends power from power lead Ha through lead 214, relay RYZ-Fi, wire 255, the contacts of relay 24, wire 264, and back to the other side I Ib oi the line by way of wire 263. The contacts of relay RY25 are therefore closed, connecting source unit input lead 210 to wire -2 B3 and thence to one side of the power line, and connecting the other source unit lead 2`l'l through the other set of relay contacts to wire 262 and so to the other side oi the power line. The source unit is thus energized, and will remain energized 'until RYI t is deenergized upon the termination operation, as previously described, and which results in de-energization of relay RY24, opening the circuit to relay RYZE, and thus disconnection of the source unit from the power mains.

The energization of relay RYZI upon starting of the source unit occurs as follows, Current flowing through starting switch SI1 passes through wire 2th, the coil of relay RYZS, Wire 221, contacts of relay RYZE and wire 263 to the opposite side oi the line. Ilnergization of relay RYBii then connects lead 239 from one side H53 of a llevolt power line through the contacts of RYZB to lead 2821, thence via branch lead 282 to the coil of RYZI, and thence via wire 284 and lead :l i2 back to the other side Il oi the 1l5-volt power line. The coil of relay EYES is energized through substantially the same circuit, being connected in parallel with the coil oi RYZI, as is apparent in the drawings. Starting of the source unit accordingly closes RYZ I, which remains locked closed by locking device |96, and at the saine time closes the contacts of relay RY2IJ, the latter action operating through lead IBI and the normally closed full scale recorder switch S5 to energize relays RYL as already described.

Preferably, provisions are made for a manual reset to the ready-tooperate position. A double pole, double throw manual switch S|3 is provided, one arm o which is connected by lead 2te to l15- voit power lead 63, and the other arm of which connected by lead 29| to 22B-volt power supply lead ist. The normal position or this switch S|3 closed with the contacts to which are connected leads 292 and 293, the rst of which leads to the coils of relays RYIS` and RY4m, and thence to ground. Lead 293 connects to the release coil i'or relay RYZI, the circuit being completed by lead 2|2 connecting back to l15volt power lead |34. Lead 293 however, contains a pair of contacts of normally-open double-pole manual reset switch SI1-l, so that the circuit lead 2% is normally open. It will be seen that closure or reset switch SHI, with switch S|3 closed to the right hand pair of contacts, as viewed in Figure l, re sults in release of relay RY, and in the periorniance of the various previously described lfunctions which occur upon release of relay. Reset switch SM, when operated, also closes contacts in a circuit lead Id between lead 235s and the 28-volt power line lead |55, which results in performance of the homing action of stepping selector switch Si, as previously described to occur under the control of the automatic reset switches. The system can accordingly be reset manually by operation of the reset switch SUI.

Figure 7 shows a fragmentary portion of a strip chart record of a typical analysis of stainless stecl by the system of the invention. The line 3GB is the line traced by the recorder pen while the internal standard phototube Pi is charging condenser' Cil to full scale deilection of the recorder pen, the phototube Pi being assumed to be operating under excitation by an iron line. The short vertical line 30|represents the dwell before the recorder switch S4 pulses the system ahead one step to connect the rst condenser Cls to the amplier to have its charge measured by the re-Y corder,- The slightly inclined pen line 3D2 represents'the motion of the pen back to the position corresponding to the charge on this condenser CIS, the incline resulting from the continuous drive of the strip chart; the short vertical line 303 then represents the dwell with the charge on CIS being recorded, prior to the next pulsing action by operation of S4. The chart represented in Figure 7 assumes the employment oi four phototubes such as PS, and four parallel channels leading to four storage condensers CIS, as in a typical practical adaptation of the invention. The chart thus shows an analysisuof stainless steel to include certain percentage concentrations of chromium, nickel, manganese and silicon. By making plots of concentrations of known samples Vs. recorder readings, percentage scales can be set up from which the concentrations can be .read directly, and such concentration scales are shown to be printed directly across the strip chart paper. It is obvious that these scales must be printed at spacings along the length of the paper strip in correlation with the advance of the strip forieach operation of recorder pulsing switch S4, and also that the elements to be analyzed must appear in the channels of the system in the same order as they are printed on the strip chart paper.

Figure '1 also illustrates the record obtained when the zero point.of the concentration scale is placed oiiscalefy lwith the range of interest expanded over the scale range on ther paper.

Thus .the chromium scale begins with a concentration of at the left hand edge of the strip chart, and .ends with at the right hand edge thereof. It will be recalled that the zero point of the scale is under the control of the resistors Rl I, while the sensitivity, or in yother words, the proportionate part of the scale -that will appear on the chart, depends upon the adjustment of the sensitivity control resistors R8 and attenuators R2. L L

Owing to changes in tube sensitivity, etc., the calibration of the system changes slowlyk over a period of time. Provision is madefor recalibration, when required, as follows. SwitchS|3 is thrown to the left, as Viewed in Figure l, so as to de-energize relays RYII, and so that its lower switch arm closes with a circuit lead 320 leading to a relay RYIE, and thence via lead 32| topower lead |64. The de-energization oi relays RY4 acts to connect condensers C2S and C2111 into the circuit in place or condensers CIS and `Clm.-` The energized relay RYIS is locked closed by relay lock 322.l Energization of relay RYIS opens circuit |65, |66, preventing running of the chart drive motor 58 owing; to the` resulting impossibility of energizing RYIS.

A standard sample with a known low concentration oi a selected element is then run in the normal fashion, except that switch S|3 is positioned to the left. The charge integration period is again under the control of the charging of C'Ii and the charge terminating function of the recorder at full scale deflection. In this run, condenser C2S will be charged instead of the condenser CIS. Without recording this Voltage, another run is then made with a high or larger known concentration of the element, the switch S|3 at this time being positioned to the right, so that condenser CIS is charged. ,i The selector relay is stepped to the channel to be calibrated, which can be accomplished by operation of manual switch S9. By then alternately energizing and cle-energizing relay RY4 through operation of switch SI3, the Voltage on either Acondenser may be' read on `the recorder, and the zerqand sensitivity controls adjusted until both samples read correctly on the calibrated concentration scale on the strip chart paper for the element in question. The system is then ready to continue analysis of unknown samples. When the source unit is again started, the previously described energization of relay RY23 will operate through its contacts', lead 28|, the relay coil 33B, for relay RY|8,'and lead 33|, to energize coil 339 and so release the relay lock 332, so that relay RYIS goes back to its normal condition, with its contacts closed.

f'Fory some purposes, it is desired to read the instantaneous rather than the integrated interi'sity` of 'aspectral line, and when this is the case, switch SIB is thrown to its alternate position, so as to energize lead 334 rather than the lead 220 going tothe relay RY3. This lead 334 energizes a relay RY6, and its contacts connect a high resistance resistor R4 between amplier input lead 30 and ground. The voltage developed across this resistor as a result of current flow fromthe phototube ris impressed on the control grid of the amplier tube 32. The system thus operates on Vinstantaneous values of the output oflv the phototube, rather than on integrated totals obtained over a period of time.

` The. slit mounting and adjustment system has several unique features which will now be described. Each slit group'ris mounted in a rectangular frame 350 (Figures,35)which is located on and adjustable along the Rowland Circle ,(focal curve). The slits I3 and I4 are formed by spaced vertical bars 35| :(Figures 4 and 5) furnished top and bottom with mounting blocks 352 which are slotted to slide along parallel mounting strips 353, being equipped with set screws 354 adapted to be set against said strips when the slit bars are in individually adjusted positions on the frames. The top part 359 of each frame is Ahorizontally slotted at 360 to receive guide pins 36| projecting from a stationary mounting 362,. and is provided with a central horizontal elongated slot 363 adapted to receive a shouldered guide screw 364 by which the frames are screwed to said mounting. Frame part 359 is also, slotted at 310 to receive lug 31| projecting from mounting`362, said lug being equipped with a .spring-pressed ball 312 adapted to bear against theadjacent surface of the slot to urge the frame to move in one direction on the guide pins 36| andl screw 364. An eccentric 315 in a slot 31B inthe top part 359 of frame 3|l0-holds the frame againstV the pressure of the spring-pressed ball and a'djustment'of this eccentricby means of a shaft 318 rotatably mounted in` mounting 362 and provided'at the top with an operating knob 319 functions to adjust the entireframe in a horizontal direction along the focal curve. A mask 311 is preferably used to close the spaces between the pairs` of slit bars.

Due to vibration and temperature changes, as wellr as aging in the frame parts of the machine, such a slit assembly will not stay in alinement with the spectral'lines over long periods oi time. In order to determine when misalinement has become suiiicient to require correction, the monitorV slit |4,.phototube Pm, and relay channel leading to condenser Cm have been provided. AAs already described, each slit I3 is originally individually adjusted so that the desired line falls through the center of the slit. The monitor slit I4, however, is so-adjusted that the center of a strong line oi? an internal standard elementA coincides with the edge yof the slit. .'.I'hus, referring to Figure 8, spectral lines 380 are alined with the centers of the slits I3, while the center of spectral line SSI is alined with one edge 382 ofmonitor slit I4. Thus a slight motion of the spectrum with respect to the slit frame gives a large change of intensity on the phototube Pm corresponding with the monitor slit I4, and this intensity is used in the usual manner to charge up the condenser CIm, vand is subsequently recorded onthe strip chart paper, this reading coming, if desired, at the'end of therun of the recording of the sample concentrations being analyzed. In practice, a .003 displacement of the slit I4 with respect to the spectral line 38| may give full scale recorder deiection. Withthe indicated slit widths, .001 represents the allowable deviation. By recording the intensity of the light falling through this monitor slit each time an analysis is made (or less often if the system is sufficiently stable) displacements of less -than .0001 can be easily detected and the individualframes realinedmanually by operation of the adjustment knob 319, before `misalinernent becomes sufliciently serious to aiect analytical accuracy. Referring again to the'strip chart shown in Figure 7, the Vertical recorder pen mark 400 represents the recording of the charge accumulated on the condenser charged by monitor phototubePm during a normal run rlhis mark 400 will be seen to fall in this casecloseto' the center chart line 5. Ad- ,iustmentsare so madefthat with `zero misalinementof the monitor slit,the`recorder pen mark would fall exactly on the center chart line 5. According to a present embodiment of the invention, the'mark 400 would fall between chart lines '4 and '5 for tolerable misalinements, with any position in between these lines acceptable. In particular, in the ,present embodiment, the adjustments are such that slit misalinements of .0004" will throw the recorder line'400 as far off as chart lines 4 and '6. As already stated, a deviation Vof .001" is about'the maximum that can be tolerated, so the system is kept on the safe side by maintaining the operation between lines 4 and 6.

The system preferably includes certain additional manual switches as`follows: Switch SID, normally'open, operates when'closed to form a circuit' from 2li-volt power line I43 via lead 394 to the coil of relay RY'I, said relay thereupon cutting out the automatic `zero correction circuit for special test purposes. VSII and 'SI2 are push switches connected into the system to manually start and 'stop the recorder chart drive motor for test purposes.

The invention has been heretofore described with the use of an internal standard line (e. g., an iron line in the case 'of an analysis of an alloy steel) for illumination of the phototube'Pi employed to charge the condenser C Il up to the value at which the charge integration period is to be terminated. As an alternative, the primary refiected beam from the spectrograph grating may be used in place of the internal standard line. Figure shows diagrammatically the sample excitation source, spark or arc, before source slit tythe spherical grating at g, and the so-called Rowland focal plane circle at R. In accordance with known principles,with the source slit t located on the circle R, spectral images of slit 't will be formed in light of different wave lengths along the circle R. In accordance with the first described form of the invention, a slit'such as I3 may be alinedwith an internal standard spectral lineyandother slits I3'maybe alined with other spectrallinesof interest. Notall the light from source slit t is dispersed by the grating, and there is accordingly -a reilected, white light primary beam which forms an image on the Rowland circle, and this image line may be caused to fall on a-slit vsuch `as M, and used as an `internal standard line in place of anvinternal standard spectral line. Thus,-the phototube Pi of Figures l and 2 in such case receives light from a slit such as M recei-Vingthe white light image of the source-slit t. It is found in practice that there is actually no -necessity for *focussing the refiected image to eliminateunwanted parts of the spectrum. Therefore, Pi can, if desired, be placed much closer to the grating, it being only necessary that it be in the path of the reiiected beam. Accordingly, We may use, for the purpose of the phototube Pi, either an internal standard spectral line, the internal standard line resulting from the primary reiiectedlbeam, or the reflected beam itself without bringingfthe latter first to an image.

The system preferably .employs a strip chart recorder, as described, :but .instead of the recorder, a .visual indicating'meter, e. g., a voltmetenmay be employed. The type of recorder hereinbefore described, in fact, has a :visual indicator scale andan indicator or pointer .which travels with the recorder pen. While Figure ..6 shows the rearward iside .of the recorder, .and henceiis/not well adapted .to illustration .of fthe visualscale, the rearwardsidelof the. scale mounting plate appearsinzsaid figure at4l0, andan indicator hand, moving with the recorder pen, at 4I I.

While We do lnot wishto `beunderstood as limit- .ing the invention, we..mayrgive thefollowing circuit element constantsas having beenfound successful in practice:

C5-210 afd. RI-lOOO ohms HL2-'1' megohm RII-10000 ohms 'RIZ-5000 ohms RIB-250 ohms R14-200 ohms Rik-20 megohms RIS-86000 ohms The system now disclosed is .of course for illustrative purposes only, rand various changes in design, structure, Sandlcircuit arrangement can be made without departing from the spirit and scope of fthe invention as Ideiined by the appended claims.

`VWe claim:

1.1In a spectrochemical analysis system, the combination of: e a phototube adapted to receive lightfroma spectral line, a condenser, means for connecting said phototubeto said condenser to'charge said condenser during a charge integration period, a `bridge thermionic ampliiier including in one arm an ampliertube having an input 'control grid `and including in an opposed arm a second amplier tube having a control grid, amplier "output leads connected across saidbridge amplifier, `a recorder connected to said output leads including an indicator movable along ascalehaving azero position, automaticzero control means connected to the control 'gridof vsaid second amplifier tube, said zero control means being operative in consonance Withfluctuations of .said indicator of said re- Acorder Lfrom its zero position to change the 21 voltage on, said controlV gridin apmannerfzto vary. the amplifier output so as to return said indicator toward its zero position, means for rendering said automatic `zero control means inoperative at the beginning of said charge integration period, and means operative at the end of. said integration period for disconnecting the charged condenser from said phototube and connecting it to said control grid of said Afirst mentioned amplifier tube. -2.7In a spectrochemical analysis system, the combination of a phototube adapted to receive light from a spectral line, a condenser, means for connecting said phototube to saidV condenser to charge said condenser during a charge integration period, a bridge thermionic amplifier including in one arm an amplifier tubel having an input control grid and including in an opposedarm a second amplier tube having a control grid, amplifier output leads connecting across said bridge ampliiier, a recorder connected to said output leads, automatic zero control means connected to the control grid ,ofsaid second amplier tube to stabilize the output of said amplifier, means for rendering said auto: matic zero control means inoperative atth,e beginning of said charge integration period, and meansv operative yat the end of said integration period for disconnecting the charged condenser from said phototubeand connecting it to said controlgrid of s aid first-mentioned amplifier tube.

3. A combination as defined in claim 2, including also a voltage adjusting potentiometer connected in shunt across the amplifier output circuit. l

4. In a spectrochemical -analysis system, the combination,with a light dispersing system before a sample exciting light source, of: a first phototube arranged to receive light from said light source, a slit arranged inv alinement With a spectral line of the spectrum formed by said light dispersing system, a second phototube ar-A ranged to receive light from said slit, iirst and second condensers, means for connecting said first and `second phototubes to said first and second condensers, respectively, to be charged by said phototubes, a high impedance amplifier including an input amplifier tube with a control grid and having an output circuit, a strip chart pen recorder having input terminals connected across the output circuit of said amplier and having a pen Vmovable across a strip chart between zero and full scale positions in response to the voltage impressed across said input terminals, motor means for advancing said strip chart, a pulsing switch intermittently actuated by said motor means, an integration termination switch actuatedv by said recorder upon said recorder pen reaching full scale position, a solenoid-actuated multiple contact stepping switch actuated stepby-step by successive energizations of said solenoid, circuit means for energizing said solenoid upon actuation of said pulsing switch, first and second position contacts on said stepping switch, said stepping switch being initially closed with said first position contact, circuit means including said first position contact for connecting said first condenser to said control grid of said amplifier when said selector switch is closed with said first position contact, circuit means controlled by said integration termination switch of said recorder for disconnecting said condensers from said phototubes upon full scaledeilection ofsad recorder pen, circuit means alsocontrolled by said,integrationtermination switch` for oper-e a ating said motor means for saidstrip chart, the solenoid of said stepping switch being actuated by said pulsing switchupon operation of said motor means, stepping said stepping switch to its second position contact, and circuit means including said second position contact of said steppingswitch forv connecting said second condenser togsaid control grid of said'amplifler.

5. Ina spectrochemical analysis system, thel combination, with ajlight dispersing system be-` fore a sample exciting light source, of a first phototube, arranged to receive light from said lightsource,1a'slit arranged in alinement with a spectral lineof Vthe spectrum formed by said light dispersingsystem, a second phototube arranged to receive light from said slit, first and second condensers, means for connecting said first and second phototubes to said rst and second condenser-s, respectively, to be charged by said phototubes, a high impedance amplifier including an input amplifier tube with a control grid and having an output circuit, a strip chart pen recorder V having input terminals connected across the output circuit of said amplifier and having a pen movable across a strip chart between zero and fullscale positions in response to the voltage impressed across said input terminals, motor means for advancing said strip chart, a pulsing switch intermittently actuated by lsaid motor means, an

integration termination switch actuated by said recorder uponv said recorder pen reaching full scale position, a solenoid-actuated stepping selector switch including a plurality of gangedmultiple-contact switches actuated step-by-step by successive energizations of said solenoid, circuit means for energizing said solenoid upon actuation of said pulsing switch, said multiplecontact switches including rst and second position contacts, and being initially closed with said first position contacts, variable sensitivity control resistors adapted to be connected across the recorder input terminals, circuit means in connection with one of said multiple-contact switches for selecting different sensitivity control resistors at different switch positions and connecting the same across said recorder input terminals, circuit means including the first position contact of the other multiple contact switch for connecting saidA first condenser to said control grid of said amplifier when said other multiple contact switch is closed with its vrst, Iposition contact, circuit means controlled by said integration termina'- combination, with a light dispersing system be-,

fore afsample exciting light source, of: a iirst phototube arranged to receive light from saidlight source, a slit arranged in alinement with a spectral line of the spectrum formed by said light dispersing system, a second phototube arranged to receive light from said slit, first vand second cndense'rs means fer @meeting Said fusi ,and

dormirse second phototubes Ito said .nrs-t and second'rcondensers,:respectively, to be` charged `by said-phototubes, a high impedance Abridge .amplifier including an .input amplifier tube with a control grid in .one arm and a second amplifier .tube with acontrol grid inanotherarm, an amplifier output `circuit 4connectedacross said bridge ampliiier, `.a `strip chart vpen recorder having input terminals connected across the output circuitof said amplifier and having a pen movable across a strip chart between zero and full scale positions in .response to the voltage impressed across said input terminals, motorfmeans for advancing said stripchart, a pulsing switch intermittently actuated .by said motor means, an integi'ation termination switch actuated .by said recorder upon said recorder pen reaching full scale position, a solenoid-actuated stepping selector switch including a plurality of ganged multiple-contact switches actuated step-by-step by successive energizations of said solenoid, circuit means for energizing said solenoid upon actuation of said pulsing switch, said multiple-contact switches including flrstand second position contacts, and being initially closed with said nrst position contacts, variable sensitivity control resistors adapted to be connected across the recorder input terminals, .circuit means in connection with one of said multiple-contact switches for selecting different sensitivity control resistors at different switch positions and connecting the same across vsaid-recorder input terminals, a zero control circuit for said bridge amplifier connected to vthe control grid for its second amplifier tube, said circuit including a source of voltage and a plurality .of selective variable zero control resistors adapted to adjust the voltage applied to said control grid of said second tube, circuit means in connection with the second of said multiple-contact switches for selecting different zero control resistors at different switch positions and connecting the same into the Zero control circuit, circuit vmeans including the first position contact of another of said multiple contact switches for connecting said first condenser to the control grid of the nrst mentioned amplier tube when said last mentioned multiple contact switch is closed with its first position contact, circuit means controlled by said integration termination switch of said recorder for disconnecting said condensers from said phototubes upon full scale deflection of said recorder pen, circuit means also controlled by said integration termination switch for operating said motor means for said strip chart, the solenoid of said stepping switch being actuated by said pulsing switch upon operation of said motor means, stepping said stepping switch to its second position contacts, and circuit means including the second position contact of the last mentioned multiple contact switch for connecting said second condenser to said control'grid of said input amplifier tube.

7. In a spectrochemical analysis system, the combination, with a light dispersing system before a sample exciting light source, of: a rst phototube arranged to receive internal standard, light from said light source, a slit arranged in alinement with a spectral line of the spectrum formed by said light dispersing system, a. phototube arranged to receive light passing through said slit, a condenser to be charged by the iirst mentioned phototube, a pair of condensers to bei charge alternately by the second mentioned phototube, a high impedance amplifier having input and output circuits, a recorder connected lil across isaid amplifier output acircuit, ay `recorder sensitivity .control .potentiometer kshunted-across said amplifier output circuit, means Afor connecting the first mentioned condenser yand one condenser of said :pair'to the .corresponding phototubes .to be icharged'thereby during a charging period, means for connecting .said ,rst `mentioned condenser .and the other condenser of said pair tothe corresponding phototubes-,to be charged thereby during a, second charging period, means for connecting the rst mentioned .conldenser to theampliiier input circuit` during each of .said charging periods, means for terminating said chargingperiods upon said recorder `recording a predeterminedcharge accumulated on said first mentioned condenser, means for thereupon disconnecting vsaid rst mentioned condenser from said amplier lfollowing said `charging periods, and means `for .thereafter connecting the indi-vidual condensers ofsaidcondenser pair Ialternately to said amplier 'input circuit.

8. In a spectrochemical analysis system, having a `focal plane .in which spectral lines lare formed, the .combination of: a slit frame positioned in said .focal plane, said `frame havinga plurality of slits spaced to receive light `from a plurality of spectral lines, said slits including :a plurality of slits spaced on said frame :to be-substantially .centered with said lines, and *including also a monitor kslit positioned-on said frame with vone of its edges ybetween the edges of its spectral line, means for adjusting the position of said frame and slits as a unit along the focal l plane, phototubes receiving vthe-light from said slits, fcondensers andcircuit means for connecting said condensers to respective phototubes, and means for recording the charges accumulated on said condensers during a common integration period.

9. In a spectrochemical analysis system, having a focal plane in which spectral Alines are formed, the combination of.: a slit frame positioned in said focal plane, said frame having a plurality of slits spaced to receive light from 'a plurality of vspectral lines, said slits including a plurality of slits spaced on said frame to be substantially centered with said lines, and including also a monitor slit positioned on said frame with one of its edges between the edges lof its spectral line, means for adjusting the position `of the frame and slits as. a unit along the vfocal plane, phototubes receiving light from the slits., and means for detecting lateral travel between the spectral lines and slit frame in accordance with `v changes in intensity of the light reaching the phototube associated with said monitor slit.

l0. In a spectrochemical analysis system, the combination, with a light dispersing system before a sample exciting light source, of: a iirst phototube arranged to receive `internal standard light from said light source, a sample analysis slit arranged in alinement with a spectral line of the spectrum formed by an element of unknown concentration in the sample, a monitor slit arranged with one edge between the edges of an internal standard spectral line of said spectrum, a slit frame supporting both of said slits arranged for adjustment movement along said spectrum, phototubes arranged to receive light passing through said slits, a condenser for each of said slits to be charged thereby, an amplier having input and output circuits, said amplifier having an ultra high input impedance, whereby it may be connected to the condensers without perceptibly discharging the con'densersl a recorder connected across the amplifier output circuit, means for connecting the condensers to respective phototubes to be charged thereby during a :charging period,. means for connecting the condenser corresponding to the first mentioned phototube across the input circuit of said amplifier, means for terminating said charging period upon said recorder recording a predetermined charge on said condenser which is connected to the ampliiier during the charging period, and for disconnecting said condenser from said amplifier, and means for thereafter consecutively connecting the remaining condensers to said amplifier to have their charges consecutively recorded by said recorder. 'f

l1. In a spectrochemical analysis system, the combination of: a bank of detectingdevices arranged to receive electromagnetic spectral beam radiation corresponding to a plurality of unknown elements in an energized sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radial tion received thereby, a-corresponding bank of of said charge integration-period, an amplifier having 'input and output circuits, said amplifier' having an ultra high input impedance, whereby it may be connected to the condensers` without perceptibly discharging the condensers step-bystep switch and circuit means for consecutively and intermittently connecting said condensers to said input circuit of said amplifier after the termination of said charge integration period,

, and a recording instrument connected to the output circuit of said amplifier, said recorder including means coordinated with said step-bystep means for making consecutive recordings representative of charges borne by said condensers during periods of rest of said step-by-step means.

12, In a spectrochemical analysis system, the combination of: a bank of detecting devices arranged to receive electromagnetic spectral beam radiation corresponding to a plurality of unknown elements in an energized sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radiation received thereby, a corresponding bank of charge integration condensers, circuits for conducting the output currents of said detecting devices to respective condensersV to accumulate electric charge thereon corresponding directly to the integrated radiation received by said detecting devices during a common charge integration period, normally open switch means in connection with said circuits operable to close said circuits from said detecting devices to said condensers at the beginning of said charge integration period, and t open said circuits at the termination of said charge integration period, an amplifier having input and output circuits, said amplifier having an ultra high input impedance, whereby it may be connected-to the condensers without perceptibly discharging the condensers, step-by-step switch and circuit means for connecting oneA of lsaid loo ndensers to said input circuit of said amplifier throughout said charge integration period, and operable automatically upon attainment of a predetermined charge to disconnect said one of said condensers from said amplifier input circuit and to consecutively and intermittently connect the remainder of said condensers to said amplifier input circuit, and a recording instrument connectedy to the output circuit of said amplifier, said recorder including means coordinated with said step-by-step means for making consecutive recordings representative of charges borne by said condensers during periods of rest of said step-by-step means.

13. In a spectrochemical analysis system, the combination, with a light dispersing system before a sample exciting light source, of: a rst phototube arranged to receive light from said light source, a slit arranged in alinement with a spectral line of the spectrum formed by said light dispersing system, a second phototube arranged to receive light from said slit, first and second condensers, means for connecting said first and second phototubes to `said rst and second condensers, respectively, to be charged by said phototubes, an amplifier including an input circuit and an output circuit, said ampliiier having an ultra high input impedance, whereby it may be connected to the condensers without perceptibly discharging the condensers a recording instrument connected to the output circuit of said amplier, a solenoid-actuated multiple contact stepping switch, circuit means for energizing said solenoid including a pulsing switch, rst and second position contacts on said stepping switch, said stepping switch being initially closed with said first position contact, circuit means including said first position contact for connecting said first condenser to said input circuit of said amplifier when said selector switch is closed with said first position contact, and circuit means operable after the termination of a predetermined condenser charging period for disconnecting said condensers from said phototubes and for actuating said pulsing switch to energize said solenoid.

14. In a spectrochemical analysis system, the combination, with a spectrum forming light dispersing system positioned before a sample exciting light source, of: a first photoelectric device arranged to receive a quantity of internal standard light from said light'source proportionate to the intensity of said source while a sample is being excited, a light slit arranged in alinement with a spectral line of said spectrum corresponding to an element of unknown concentrationy in the sample, a second photoelectric `device arranged to receive light from said slit, first and second charge storage condensers, means for connecting said first. and second condensers to said first and second photoelectric devices, respectively,- to be charged thereby during a controlled common charge integration period, a voltage amplifier of ultra high input impedance adapted circuiting of ultra high shunt. impedance for connecting the input end of said ultra high impedance amplier across said rst condenser throughout said charge integration period, means arresting the charging of said condensers to terminate said charge integration period coincidentlyvvith full scale deflection of said recorder element, and said condenser switching means and lcircuiting including means `operable upon termination of the charge integration period to disconnect said amplifier from said first condenser and to connect it across said second `condenser.

15. In a spectrochemical analysis system, the

I combination, witha spectrumv forming light` dis-A persing system positioned before a sample exciting light source, of t a first photoelectric` device arranged to receive a quantity of internal standard light' from said light source proportionate to the intensity of said source while a sample is being excited, a light slit arranged in alinement with a spectral line of said spectrum corresponding; to an element of unknown concentration in the samplea second'. photoelectric device arranged to receive light from said slit, nrs-t and l second charge storage condensers, means for connecting said iirst and second condensers to said first. and secondphotoelectric' devicesrespectively, to be charged''therebyy during a controlled common charge integration period, anv amplifier adapted to be connected consecutively across said condensers, saidamplifier having an ultra high input impedance, so as to avoid perceptible discharge of the condensers, a strip chart. recorder for recording the output from said ampli'lier, said recorder havingl a recording element movable transversely-acrossa longitudinally movable strip chart between zero and full scalel position in response tothe amplitude` of theoutput of said amplier, condenser switching means and circuiting of ultrahigh shunt impedance fon connecting the input end of said. ultrahigh impedance amplifier across said first condenser throughout said charge integration period, means arresting the l charging of said condensers to' terminatefsaid charge integration period coincidently with full scale deection of said recorder' element', andsaid condenser switching means and circuiting including meansoperable upontermination of the charge integration period to disconnect'saidam- Y pliier from said first condenser and' to connect the strip chart recorder at full scale deflection of the recorder element.

19. The subject matter of claim 18, wherein the means operable upon terminationY of the charge integration period to disconnect the am.- plier from the rst condenser and connect it across the second condenser includes switching means operated by the strip chart recorder at full scale deflection of the recorder element.

20. In a spectrocher-nical analysis system, the combination, with a spectrum forming radiation dispersing system positioned before a sample excited by a source of electromagnetic radiations, of a first detecting devicel arranged to receivey a quantity of internal standard radiation from said source proportionate to the intensity of said source while a sample is being excited, a bank 0i detecting devices arranged to receive spectral lines of said spectrum corresponding to elements of `unknown concentration in the sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radiation received thereby, a plurality of slit means combinedl with said dispersing system for controlling the radiation transmitted by the dispersing system to the individual detecting devices, a first storageVV condenser and a bank of storage condensersy means for connecting said rst storage condenser across the: first detecting device and the bank of condensersacross respective members, of. said bank of detecting devices during a commonicharge integration period, an amplifier adaptedfto be connected consecutively. acrosswsuccessive condensers, said amplifier having anA ultra high input impedance, so as to avoid'perceptible discharge of the condensers, a strip chart recorder'for recording the output from said amplifier, said recorder having a recording element movable transversely across a longitudinally movable strip chart between zero and vfull scale position in response to the amplitude oi theoutput of said ampliiier,.means arresting thecharging of the condense-rs to terminate said charge integration period upon the charge stored in said firstlcondenser attaining a predetermined value, and step-by-step condenser switching means and circuiting of ultra high shunt impedance operable upon termination of said charge integration period to connect said amplifier across each: of the condensers of said bank of condensers in turn.

21. In a spectrochemical analysis systennthe combination, with a spectrum forming radiation dispersing'system positioned before a sample excited by a source of electromagnetic. radiations, of: a rst detecting` device arranged. to receive a quantity of internal standard light from said light source proportionate to the intensity of said source while a sample is being excited, a bank of detectingy devices arranged to receive spectral lines of said spectrum corresponding to elements of unknown concentration in the sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radiation received thereby, a plurality of slit means combinedwith said dispersing system. for controlling the radiation. transmitted by the dispersing system to the individual detecting devices, a first storagecondenser and a bank of storage condensers, means for connecting said rst storage condenser across the first detecting device.v and the bank'of condensers across respective mem.- lbers of said'bankof detecting. devices during a common'charge integration perioden amplier adapted to be connected consecutively across successiveA condensers, said amplier having an ultra high input impedance so as to avoid perceptible discharge of the condensers, a recorder for recording output from said amplier while said amplier is connected toV successivecondensers o1' said bank, means arresting the charging of the condensers to terminate said charge integration period upon the charge stored in said iirst condenser attaining a predetermined value, andstep-by-step condenser switching' means and 29 able upon termination of saidicharge integration period to connect said-amplifier across each of the condensers of said bank of, condensers in 22. In a spectrochemical analysis system, the combination, with a spectrum iormingradiation dispersing system positioned before a sample excited by a source of electromagnetic radiations, of: a first detecting device arranged to receive a quantity of internal standard radiation from-said source proportionate to the intensity of said source while a sample is being excited, a bank of detecting devices arranged to receive spectral lines of said spectrum corresponding to elements of unknown concentration in the sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radiation received thereby, a plurality of slit means combined with said dispersing system for controlling the radiation transmitted by the dispersing system to the individual detecting devices, a bank of storage condensers, means for connecting the bank of storage condensers across respective members of said bank of detecting devices during a common charge integration period, an amplier adapted to [be 'connected consecutively across successive condensers, said amplier having an ultra high input impedance, so as to avoid perceptible discharge of the condensers, a strip chart recorder for recording the output from said amplifier, said recorder having a recording element movable transversely across a longitudinally movable strip chart between zero and full scale position in response to the amplitude of the output of said amplifier, means responsive to and operable by virtue of attainment of a predetermined integrated output from said first detecting device for arresting the charging of said condensers, and step-by-step condenser switching means and circuiting of ultra high shunt impedance operable upon termination of said charge integration period to connect said amplifier across each of the condensers of said bank of condensers in turn.

23. In a spectrochemical analysis system, the combination, with a spectrum forming radiation dispersing system positioned before a sample excited by a source of electromagnetic radiations, of a first detecting device arranged to receive a quantity of internal standard radiation detecting from said source proportionate to the intensity of said source while a sample is being exicted, a bank of detecting devices arranged to receive spectral lines of said spectrum corresponding to elements of unknown concentration in the sample, said detecting devices being adapted to deliver output L current responsive to the quantity of radiation received thereby, a plurality of slit means combined with said dispersing system for controlling the radiation transmitted by the dispersingsystem to the individual detecting devices, a bank of storage condensers, means for connecting the bank of storage condensers across respective members of said bank of detecting devices during a common charge integration period, an ampliner adapted to be connected consecutively across successive condensers, said amplifier having an ultra high input impedance, so as to avoid perceptible discharge of the condensers, a recorder for recording output from said amplifier While said amplier is connected to successive condensers of said bank, means responsive to and operable by virtue of attainment of a predetermined integrated output from said first detecting device for arresting the charging of said condensers, and T5 30 step-'by-'step condenser switching 'means and circuiting of ultra high shunt impedance operable upon termination of said charge integration period to'connect said amplifier across each of the condensers of said bank of condensers in turn.

24.r In a-spectrochemical analysis system,-the combination, with a spectrum forming radiation dispersing systemf'positioned before a sample excited'by a source of lelectromagnetic radiations, of 'a first detecting device arranged to receive a quantity of internal standard radiation from said source proportionate to the intensity of said source-while a sample is being excited, a bank of detecting devices arranged to receive spectral lines of saidspectrum corresponding to elements of unknown concentration in the sample, said detecting devices being adapted -to deliver output currents responsive to the quantity of radiation received thereby, a plurality of slit means cornbined with said dispersing system for controlling the radiation transmitted by the dispersing system to the individual detecting devices, a rst storage condenser and a bank of storage condensers, means for connecting said first storage condenser across the rst detecting device and the bank of condensers across respective members of said bank of detecting devices during a common charge integration period, an amplifier adapted to be connected consecutively across successive condensers, said amplifier having an ultra high input impedance, so as to avoid perceptible discharge of the condensers, a strip chart recorder for recording the output from said amplifier, said recorder having a recording element movable transversely across a longitudinally movable strip chart between zero and full scale position in response to the amplitude of the output of said amplier, condenser switching means and circuiting of ultra high shunt impedance for connecting the input end of said ultra high impedance amplifier across said first condenser throughout said charge integration period, means arresting the charging of said condensers to terminate said charge integration period coincidently with full scale deiiection of said recorder element, and said condenser switching means and circuiting including step-by-step means operable upon termination of said charge integration period to disconnect said amplier from said rst condenser and to connect it to each of the condensers of said bank in turn.

25. In a spectrochemical analysis system, the combination, with a spectrum forming radiation dispersing system positioned before a sample eX- cited by a source of electromagnetic radiations, of: a rst detecting device arranged to receive a quantity of internal standard radiation from said source proportionate to the intensity of said source While a sample is being excited, a bank of detecting devices arranged to receive spectral lines of said spectrum corresponding to elements of unknown concentration in the sample, said detecting devices being adapted to deliver output currents responsive to the quantity of radiation received thereby, a plurality of slit means combined with said dispersing system for controlling the radiation transmitted by the dispersing system to the individual detecting devices, a rst storage condenser and a bank of storage condensers, means for connecting said rst storage condenser across the first detecting device and the bank of condensers across respective members of said bank of detecting devices during a common charge integration period, a voltage 

1. IN A SPECTROCHEMICAL ANALYSIS SYSTEM, THE COMBINATION OF: A PHOTOTUBE ADAPTED TO RECEIVE LIGHT FROM A SPECTRAL LINE, A CONDENSER, MEANS FOR CONNECTING SAID PHOTOTUBE TO SAID CONDENSER TO CHARGE SAID CONDENSER DURING A CHARGE INTEGRATION PERIOD, A BRIDGE THERMIONIC AMPLIFIER INCLUDING IN ONE ARM AN AMPLIFIER TUBE HAVING AN INPUT CONTROL GRID AND INCLUDING IN AN APPOSED ARM A SECOND AMPLIFIER TUBE HAVING A CONTROL GRID, AMPLIFIER OUTPUT LEADS CONNECTED ACROSS SAID BRIDGE AMPLIFIER, A RECORDER CONNECTED TO SAID OUTPUT LEADS INCLUDING AN INDICATOR MOVABLE ALONG A SCALE HAVING A ZERO POSITION, AUTOMATIC ZERO CONTROL MEANS CONNECTED TO THE CONTROL GRID OF SAID SECOND AMPLIFIER TUBE, SAID ZERO CONTROL MEANS BEING OPERATIVE IN CONSONANCE WITH FLUCTUATIONS OF SAID INDICATORY OF SAID RECORDER FROM ITS ZERO POSITION TO CHANGE THE VOLTAGE ON SAID CONTROL GRID IN A MANNER TO 